This invention relates to control of electrical current for efficiency increase and protective powering of electrical motors.
Potential for increase in efficiency of electrical motors by regulation of current for their operation has resulted in a variety of motor-electric controllers for its accomplishment. None, however, computes on a microsecond basis the motor-loading needs of electrical motors for electrical current and, accordingly, optimizes the electrical current supplied for predetermined rotational speeds of the motors and, in addition, provide operational analyses and fault protection against hazzards to motors and to rotationally coupled devices in a manner taught by this invention.
Examples of most-closely related known but yet different motor-electric controllers are described in the following patent documents. U.S. Pat. No. 5,249,118, issued to Smith on Sep. 28, 1993, described input control of current for a rotational-speed controller that also controlled rate of increase and decrease of rotational speed for computer-controlled machinery. It is representative of a plurality of patents and prior art that relate to control of speed with control of input current in contrast to Applicants"" invention for optimization-control of current for predetermined rotational speed of motors. In the Smith patent, as in other variable-speed motors, current to the motors is not optimized at the variable speeds in a manner taught by this invention. Logic, methods and features for accomplishing speed control differ accordingly from the current-optimization control for predetermined speed described by Applicants.
Current control for economizing power of motors at operational speeds by control of input current with yet different logic, methods and features are described in the following patent documents. U.S. Pat. No. 4,864,212, issued to Parker on Sep. 5, 1989, described a sine wave power source connected through a triac to a control system with a gate electrode which is energized by a train (sequence) of sawtooth-shaped control signals having a repetition rate which is twice the frequency of the sine wave power source for providing short bursts of energy to decrease total power input for low power requirements at low fixed rates for variable rates of low-speed operation. U.S. Pat. No. 4,636,702, issued to Hedges on Jan. 13, 1987, described a sample transformer operative to generate a voltage pulse related to inrush-current parameters for control of portions of sine waves of power input to stator windings for diminishing electrical current to a motor during low loading. It is limited further to a xe2x80x9cmanually settable meansxe2x80x9d for selecting a maximum value of motor torque during start mode of operation. U.S. Pat. No. 4,382,223, issued to Hedges on May 3, 1983, and an improvement thereof, U.S. Pat. No. 4,414,499 issued to Hedges on Nov. 8, 1983, described use of a small AC generator coupled to a rotor of an electric motor to produce a signal for controlling a sine wave modifier to regulate current to the motor in accordance with load requirements. The load requirements were determined by a difference between an optimal RPM for the motor and an RPM indicated by the small AC generator. U.S. Pat. No. 4,341,984, issued to Parker, et al. on Jul. 27, 1982, is based on a frequency controller to produce at least two output frequencies for different speeds of operation of a motor. Other U.S. patents issued to Parker and/or Hedges, have employed variations of those indicated above.
Objects of patentable novelty and utility taught by this invention are to provide an efficiency-maximizing motor controller and method which:
provides soft starts of motors for eliminating extra power consumption, for decreasing motor wear and for decreasing wear of devices coupled to the motors from full-power, fast startups of motors. The time duration of the ramp-up is user configurable in software to suit the application;
provides consumption of bare minimum amounts of electrical power for selectively no-load and part-load operation of motors at design motor speeds in order to save up to seventy percent of electrical power required for full-load operation;
provides motor-parameter off-switching and selective on-switching for fault protection against power surges by use of semiconductor transient suppressors, power deficiencies including low and high mains voltages, motor stalling by sensing both current and phase difference between voltage and current, overload over time and based on previously acquired data known, that characterizes the motor being controlled, excessive heat or cold and other extraneous problems;
provides analyses of motor-operation factors and efficiencies by communicating comprehensive monitored parameters to a personal computer connected individually by wired or wireless means or via a network connected by wired or wireless means and running a variety of protocols listed elsewhere in this document. The following list includes but not limited to the parameters and conditions available for observation or record:
1) Mains Volts (true RMS)
2) Mains Volts DC offset
3) Mains Current (true RMS)
4) True Watts
5) Volt Ampers
6) Power Factor
7) Reactive Factor
8) Motor Volts (true RMS)
9) Motor Volts DC offset
10) Motor Peak Volts
11) Motor Peak Current
12) Motor Hours Duration Run
13) Calculation of power savings (user KWH rate selected)
14) Manual Parametric adjustment of controller
15) Manual selection of start options (soft start and random start)
16) Manual selections of Fault condition Options
17) Calibration of:
a Mains Volts
b Mains Volts offset
c Motor volts
d. Motor Volts offset
18) Power savings method selection, Managed or Fixed Voltage reduction
19) Bar graph to indicate savings using 8 LED red to indicate no savings, amber to indicate moderate savings, 6 green to indicate degree of savings e.g. all on maximum savings
20) Use of both digital and analog gauges for display decreases motor power use and costs;
decreases [w]World need and consumption of electrical power; and
can be used on both single-phase and three-phase motors and on nearly all sizes of motors for nearly all consumer, commercial and industrial applications of motors.
This invention accomplishes these and other objectives with an efficiency-maximizing motor controller and method in which an induction motor has a 40 MIPS (40 million instructions per second) digital signal processor (DSP) that calculates and optimizes supply of current for existent motor loading from a mains voltage through a current-control element. The current-control element can include a standard triac, a field-effect transistor, an insulated gate bipolar transistor, a 3 quadrant triac or other select control element together with an additional back EMF (Electro Motive Force) clamping device that is connected across the motor itself. This device has to be an IGBT or Field Effect Transistor since the DSP needs to control the on and off point of this device within the back EMF portion of the motors induction cycle every half cycle period of the mains. This novel technique assures that the energy contained in the motor (the back EMF) is contained in the motor and not returned to the mains as is presently the case. This technique obviously improves the efficiency since mains power is not used at all during the back EMF cycle. Moreover, the power factor, clearly, is improved as a result. When an IGBT or a field effect transistor is employed as the energy control element further savings are possible and a further improvement of power factor will result. Application of this class of device, as previously stated, has the ability to turn on and off under the control of the DSP. This means that, unlike the Triac or SCR (Thyristor) the energy supplied to the motor, which is the xe2x80x9carea under the curvexe2x80x9d, can be placed at a user""s discretion during the sine wave half-cycle of the mains. Such control allows a more constant power factor to be achieved, similar to the motor under conditions of direct connection to the mains, at all motor loads.
An induction motor rotating unloaded is predominately an inductor. In this state, the only work being done is to overcome frictional losses and inertial kinetic energy necessary to maintain rotation. Being largely inductive in this state, current lags voltage by nearly ninety degrees. As the motor is loaded increasingly, a phase difference of current lag diminishes. This is a change in phase angle from near ninety degrees to an angle approaching zero degrees of current lag, Accurately computed with artificial intelligence, this change in phase angle is an accurate measure of motor load for which current is required for operation at an optimum rotational speed.
This invention uses this and other motor characteristics, including DC offset and current to calculate optimum firing angles, firing durations and firing current for dynamically adaptive triacs and other control elements in order to achieve motor horsepower adaptively to its work loading at the optimum rotational speed. Digital calculation and motor-control feedback of this and other motor parameters in millionths of seconds with this invention provide motor-current optimization for all motor-use conditions of loading. Calculation of motor-load requirement for current and supply of that current are effectively simultaneous. Every calculation and control instruction are done within the half cycle period of the mains.
The above and other objects, features and advantages of the present invention should become even more readily apparent to those skilled in the art upon a reading of the following detailed description in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.